TECHNICAL DOCUMENT. Influenza virus characterisation. Influenza A(H3N2) virus analysis. Summary Europe, December Summary

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1 Community Network of Reference Laboratories (CNRL) for Human Influenza in Europe Influenza virus characterisation Summary Europe, December 2011 Summary Since week 40/2011, influenza A(H1N1)pdm09, influenza A(H3N2), and influenza B/Victoria- and B/Yamagatalineage viruses have been detected in ECDC-affiliated countries. However, the number of detections has been low and only A(H3N2) viruses and a single B/Yamagata-lineage virus have been analysed at the London WHO CC to date: Type A viruses predominate over type B. A(H3N2) viruses predominate over A(H1N1)pdm09 viruses. While A(H3N2) viruses collected since 1 February 2011 fall into seven genetic groups, all recent viruses analysed from ECDC-affiliated countries fall within group 3 and there is some evidence of altered antigenicity compared to the vaccine virus A/Perth/16/2009. Influenza B viruses of the B/Victoria/2/87 and B/Yamagata/16/88 lineages have been detected in approximately equal proportions. Influenza activity has remained low across the ECDC-affiliated countries with sporadic detections since the start of weekly reporting in week 40/2011, indicative of a late start to the influenza season compared to the season. As at week 52/2011, 807 influenza detections had been reported: 736 (91.2%) type A and 71 (8.8%) type B. Of the type A viruses, 414 were sub-typed [23 (5.6%) as A(H1)pdm09 and 391 (94.4%) as A(H3)], while the lineage of 14 type B viruses had been determined [eight (57.1%) as B/Yamagata/16/88 and six (42.9%) as B/Victoria/2/87]. Table 1 provides a summary of the 37 specimens from seven countries collected after 1 October 2011, received at the London WHO CC. At the time of this report being written, nine viruses had been recovered and subjected to antigenic and genetic analyses, eight A(H3N2) and one B-Yamagata lineage. Batches of specimens for which analysis has yet to be completed are shown as in process. Influenza A(H3N2) virus analysis For specimens collected since 1 October 2011, influenza A(H3N2) viruses have been successfully isolated and propagated from three ECDC-affiliated countries. The difficulties with antigenic characterisation of recent H3N2 viruses were described in the most recent influenza virus characterisation report. With HI assay using guinea pig red blood cells, in the presence of oseltamivir to reduce any effect of the virus neuraminidase on the agglutination of the red blood cells (Lin et al. 2010), all viruses show 4 16 fold reductions in titre against post-infection ferret serum raised against the 1

2 A/Perth/16/2009 vaccine virus compared to the homologous titre (Table 2). Similar reductions were observed with five of the other post-infection ferret sera where homologous titres of 2560 were seen, and these included sera raised against viruses in HA genetic groups 1, 5 and 6. However, reductions were not observed for sera raised against a genetic group 5 virus (A/Alabama/5/2010) that gave a homologous titre of only 160 and two genetic group 3 viruses (A/Hong Kong/3969/2011, A/Stockholm/18/2011), both of which yielded homologous titres of 640. In the last (August and September 2011) influenza virus characterisation report seven genetic groups were identified in the H3 HA phylogeny. Figure 1 shows an updated HA phylogeny in a global context: all recently circulating viruses fall within the A/Victoria/208/2009 clade, with the most recently circulating viruses (August November) located in genetic groups 3, 5 and 6. The seven EU/EAA virus-containing specimens with collection dates in October and November 2011, received at the London WHO CC and represented in the phylogeny, all fall within genetic group 3 in a sub-group defined by A198S and N312S amino acid substitutions, together with viruses from Alaska, American Samoa, Norway and Sweden, and earlier viruses from Hong Kong, Slovenia, South Africa and Thailand. Influenza B virus analyses While the number of influenza B virus detections has been low, they appear to be present in approximately equal proportions, and to date only a single B/Yamagata lineage virus has been characterised at the WHO CC. B/Yamagata-lineage viruses With HI assay, the B/England/254/2011 virus showed 8-fold or greater reductions with all post-infection ferret sera used, with the exception of that raised against B/Florida/4/2006, a previous vaccine virus (Table 3). Phylogeny based on the HA1-coding region of the HA gene shows the virus to fall in the B/Bangladesh/3333/2007 and B/Wisconsin/01/2010 genetic clade, defined by amino acid substitutions S150I, N165Y and G229D, as do the majority of recently collected B/Yamagata-lineage viruses. A number of genetic groups exist within this clade and the B/England/254/2011 virus falls within a group defined by M251V amino acid substitution, with other recently circulating viruses (August November) from Spain, Sweden and the USA, falling in a sub-group with the B/Indiana/10/2011 virus (Figure 2). Note on the figures The phylogenetic trees were constructed using neighbour-join in MEGA4. The bars indicate the proportion of nucleotide changes in the sequence. Reference strains are viruses against which post-infection ferret antisera have been raised. The colours indicate the date of sample collection. Isolates from ECDC countries are highlighted in yellow. Sequences for some of the viruses from non-european countries were recovered from GISAID and we acknowledge all laboratories who submitted sequences directly to the London WHO CC. 2

3 Table 1 Summary of specimens collected since 1 October 2011 and received by 31 December MONTH H1N1pdm H3N2 B Yamagata lineage B Victoria lineage Country Number Number Number Number Number Number Number Number received recovered received recovered received recovered received recovered OCTOBER Germany 1 in process Norway 3 in process 2 in process Sweden 1 in process 2 in process United Kingdom NOVEMBER Finland 1 1 Germany 1 in process Netherlands in process 1 in process Norway 2 in process Slovakia 2 2 Sweden 3 in process 4 in process 3 in process United Kingdom 2 2 DECEMBER Germany 3 in process Netherlands 1 in process Norway 1 in process Total Received = % of total 11% 68% 13% 8% Table 2 Antigenic analysis of A(H3N2) viruses by HI (guinea pig RBCs with 20nM oseltamivir). Post infection ferret sera Viruses Collection Passage A/Bris A/Perth A/Vic A/Vic A/Ala A/Perth A/HK A/Stock A/Iowa Date History 10/07 16/09 208/09 210/09 5/10 10/ /11 18/11 19/10 F18/07 F35/11 F7/10 F11/10 F27/10 F03/11 F27/11 F28/11 F15/11 Genetic group group 1 group 5 group 5 group 3 group 3 group 6 REFERENCE VIRUSES A/Brisbane/10/ E2/E < < < < < A/Perth/16/ E3/E1 < A/Victoria/208/ E3/E A/Victoria/210/ E2/E A/Alabama/5/ MK1/M2/SIAT A/Perth/10/ E2/E A/Hong Kong/3969/ MDCK A/Stockholm/18/ MDCK2/SIAT A/Iowa/19/ E3/E TEST VIRUSES A/England/257/ SIAT P1/SIAT A/England/256/ SIAT P1/SIAT A/England/255/ SIAT P1/SIAT A/Bratislava/31/ SIAT A/Bratislava/31/ MDCK2/SIAT A/England/258/ SIAT P1/SIAT A/England/259/ SIAT P1/SIAT A/Finland/190/ SIAT3/SIAT < = <40 Vaccine virus Sequences included in HA phylogeny Haemagglutination inhibition titre 1 Table 3 Antigenic analysis of influenza B/Yamagata-lineage viruses by HI (turkey RBCs) Haemagglutination inhibition titre Post infection ferret sera Viruses Collection Passage B/Fl 3 B/Eg 1 B/Fl 1 B/Bris 2 B/Eng 2 B/Bang 2 B/Wis 2 date History 4/06 144/05 4/06 3/07 145/ /07 1/10 SH479 F3/07 F20/07 F24/07 F09/08 F21/08 F26/10 REFERENCE VIRUSES B/Egypt/144/ E3/E B/Florida/4/ E3/E B/Brisbane/3/ E2/E B/England/145/2008 Ex/E5 320 < < B/Bangladesh/3333/ E4/E B/Wisconsin/1/ E3/E TEST VIRUSES B/England/254/ SIAT1/MDCK < 160 < < = <40; 2. < =<10 ; 3. hyperimmune sheep serum Sequence included in HA phylogeny 3

4 Figure 1 Phylogenetic comparison of influenza A(H3N2) HA genes. 4

5 Figure 2 Phylogenetic comparison of influenza B/Yamagata-lineage HA genes (HA1 coding region). 5